Utility plants often seek to remove mercury from exhaust streams in order to comply with environmental regulations. Introducing an activated carbon into an exhaust stream is a common method for removing mercury. Once the activated carbon has removed mercury, it is captured by the plant, often in the same device that captures particulate matter or fly ash.
For various cost reasons, utility plants may seek to recycle collected fly ash as an additive or component in various building materials. For example, fly ash may be used as a concrete additive. Frequently, the fly ash utility plants seeks to recycle also contains the activated carbon used for mercury removal. Certain activated carbon can remain highly active and some activated carbons have been known to compromise the integrity of concrete. In particular, various activated carbons may have an affinity to adsorb air entrainment agents, which are added to concrete to increase durability.